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Old 12-21-2011, 04:31 PM   #1
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Default Help, Astro van running bad, stumbling

1998 Awd Astro, 150,000 miles
New plugs, wires, premium (brass) dist cap, rotor, ignition coil.
Ran a couple of bottles of fuel injector cleaner and a bottle of dry gas thru it.
The above new items had no effect on curing the hesitation.
On light throttle acceleration it coughs and stumbles but eventually goes ok.
The second I tip into the gas pedal more, it takes off like mad. No issue.
It has done it some at freeway cruising steady but not all the time.
Happened for a while with no codes ever getting set.
Yesterday it finally tripped light and code was multiple random misfire.
I drove it with doghouse off and fp gauge attached. Didn't notice any major drop when it faltered. Getting upper 50'* in fp at idle, goes up some with throttle and backs down some on idle down.
I guess I have not eliminated fuel pump as the culprit.
It, so far, has not stalled or left us standard.

Any ideas? What am I missing?
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Old 12-21-2011, 05:18 PM   #2
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What about paying shop to power clean objectors?
Anyone ever have any luck with this?

This question is based on the possibility of a leaking objector flooding under low rpm then ok with more throttle.
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Old 12-21-2011, 06:51 PM   #3
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the spider injectors are a very common failure and should be upgraded to these, since youve gone through the ign. already this would be the next step.
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Old 12-22-2011, 09:13 AM   #4
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and check fuel pressure to make sure the pump hasn't started to fail.
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Old 12-22-2011, 09:26 AM   #5
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The pump in that model Astro is a very high failure item (all the 4.3L S10/ Astro, etc). The fuel pump on year year, with 150k miles, means the fuel pump, if not failing, will be soon. Note the new fuel pump will come with a upgraded electrical harness, which is the reason the original fuel pumps are failing.

Also- on the S10/ Astro the ignition switch also fails, and often reflects a failing fuel pump. I have owned many S10/Blazers and Astros, and for preventive measures I replace the fuel pump and ignition switch as part of preventative maintenance.

One last thing to look at is the ground to the fuel pump. On the S10 it is on the left side a foot from the rear tail lights. I had the stranded ground wire down to a few strands and getting dirt, causing the fuel pump to intermittenly fail on my Son'* S10. Took me two months to find it, and ten minutes to fix.
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Old 12-22-2011, 09:52 AM   #6
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he said his pressure is high 50'* which is just starting to be on the weak side, but his symptoms are of over fueling not under. the new injector assembly comes with a new fuel pressure regulator. then eventually like guns said you will need the pump assembly and clean up your wiring and ground because most go around the mileage you have.
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Old 12-22-2011, 10:12 AM   #7
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Another thought..
Possibly a throttle position sensor?
How about a dead spot at light throttle them good again with a little more throttle?
Could be same dead spot that I found with very light throttle on the freeway where again problem gone with a little more pedal.
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Old 12-22-2011, 01:34 PM   #8
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you can test it with a meter if you want, should be similar to this.
https://www.gmforum.com/trouble-shooting-test-procedures-141/testing-tps-throttle-position-sensor-279319/
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Old 12-22-2011, 01:55 PM   #9
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Thanks jwfirebird.
Going to check tps later today.

Also...
Further reading on this site and more thoughts about fuel pressure
I hooked the fp guage back up, cycled key to bring pressure up, about 57/58 psi. It did start dropping right away with key off. Down 10 psi within 15 minutes. Shouldn't it hold pressure? Back to thinking about leaking injector or poppet. Also read here of one (taxi I think it was) had a leaking or cracked injector tube/line, wasn't the poppet on his. Don't want to pull it this far apart on a hunch but might have to. Could fp leak down possibly be in tank/pump rather than in injector area?

Also why, if injector leaking causing loss of fp while shut off doesn't it act flooded upon startup?
And could the leak be enough to cause flooding/misfire with light throttle? It will not act up in park, only driving/taking off with light throttle.
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Old 12-22-2011, 03:01 PM   #10
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some good info here about what to check and how. your koeo pressure is really low but you said it stays there when running? which would be within spec. the site gives dead head pressure specs of like 70-90 psi if your pump meets that its not likely the cause, but the fpr.

http://www.tomorrowstechnician.com/A...injection.aspx

i would check the tps, and pull a plug or two see if you can see something that may narrow it down
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